linux-kernel - Re: [PATCH v3 31/41] powerpc/32: Dismantle EXC_XFER

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Date:   Tue, 3 Aug 2021 10:43:13 +1000 (AEST)
From:   Finn Thain <fthain@...ux-m68k.org>
To:     Stan Johnson <userm57@...oo.com>,
        LEROY Christophe <christophe.leroy@...roup.eu>
cc:     linuxppc-dev@...ts.ozlabs.org, linux-kernel@...r.kernel.org,
        Nick Piggin <npiggin@...il.com>,
        Michael Ellerman <mpe@...erman.id.au>,
        Paul Mackerras <paulus@...ba.org>,
        Benjamin Herrenschmidt <benh@...nel.crashing.org>
Subject: Re: [PATCH v3 31/41] powerpc/32: Dismantle
 EXC_XFER_STD/LITE/TEMPLATE

On Mon, 2 Aug 2021, LEROY Christophe wrote:

> Le 01/08/2021 à 03:21, Finn Thain a écrit :
> > On Sat, 31 Jul 2021, Christophe Leroy wrote:
> > 
> > > > 
> > > > Stan Johnson contacted me about a regression in mainline that he
> > > > observed on his G3 Powerbooks. Using 'git bisect' we determined that
> > > > this patch was the cause of the regression, i.e. commit 4c0104a83fc3
> > > > ("powerpc/32: Dismantle EXC_XFER_STD/LITE/TEMPLATE").
> > > > 
> > > > When testing 4c0104a83fc and all subsequent builds, various user
> > > > processes were liable to segfault. Here is the console log that Stan
> > > > provided:
> > > 
> > > Hi, i will be able to look at that more in details next week, however I
> > > have a few preliminary qurstions.
> > > 
> > > Can you reliabily reproduce the problem with the said commit, and can
> > > you reliabily run without problem with the parent commit ?
> > 
> > Yes and yes. (I already asked Stan to establish those things before I
> > contacted the list.)
> 
> I think I found the problem with that commit. Can you retry with the following
> change:
> 
> diff --git a/arch/powerpc/kernel/head_book3s_32.S
> b/arch/powerpc/kernel/head_book3s_32.S
> index 0a3d7d4a9ec4..a294103a91a1 100644
> --- a/arch/powerpc/kernel/head_book3s_32.S
> +++ b/arch/powerpc/kernel/head_book3s_32.S
> @@ -299,7 +299,7 @@ ALT_MMU_FTR_SECTION_END_IFSET(MMU_FTR_HPTE_TABLE)
>  	EXCEPTION_PROLOG_1
>  	EXCEPTION_PROLOG_2 0x300 DataAccess handle_dar_dsisr=1
>  	prepare_transfer_to_handler
> -	lwz	r5, _DSISR(r11)
> +	lwz	r5, _DSISR(r1)
>  	andis.	r0, r5, DSISR_DABRMATCH@h
>  	bne-	1f
>  	bl	do_page_fault

That patch doesn't apply to mainline. This version might help.

diff --git a/arch/powerpc/kernel/head_book3s_32.S b/arch/powerpc/kernel/head_book3s_32.S
index 764edd860ed4..68e5c0a7e99d 100644
--- a/arch/powerpc/kernel/head_book3s_32.S
+++ b/arch/powerpc/kernel/head_book3s_32.S
@@ -300,7 +300,7 @@ ALT_MMU_FTR_SECTION_END_IFSET(MMU_FTR_HPTE_TABLE)
 	EXCEPTION_PROLOG_1
 	EXCEPTION_PROLOG_2 INTERRUPT_DATA_STORAGE DataAccess handle_dar_dsisr=1
 	prepare_transfer_to_handler
-	lwz	r5, _DSISR(r11)
+	lwz	r5, _DSISR(r1)
 	andis.	r0, r5, DSISR_DABRMATCH@h
 	bne-	1f
 	bl	do_page_fault